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BUREAU OF MINES 
INFORMATION CIRCULAR/1989 

w/7 



A Personal Miner's Carbon 
Monoxide Alarm 



By J. E. Chilton and C. R. Carpenter 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Mission: Asthe Nation's principal conservation 
agency, the Department of the Interior has respon- 
sibility for most of our nationally-owned public 
lands and natural and cultural resources. This 
includes fostering wise use of our land and water 
resources, protecting our fish and wildlife, pre- 
serving the environmental and cultural values of 
our national parks and historical places, and pro- 
viding for the enjoyment of life through outdoor 
recreation. The Department assesses our energy 
and mineral resources and works to assure that 
their development is in the best interests of all 
our people. The Department also promotes the 
goals of the Take Pride in America campaign by 
encouraging stewardship and citizen responsibil- 
ity for the public lands and promoting citizen par- 
ticipation in their care. The Department also has 
a major responsibility for American Indian reser- 
vation communities and for people who live in 
Island Territories under U.S. Administration. 



Information Circular 9233 



A Personal Miner's Carbon 
Monoxide Alarm 

By J. E. Chilton and C. R. Carpenter 





"*""»-, 










: 




. 










' 








UNITED STATES DEPARTMENT OF THE INTERIOR 
Manuel Lujan, Jr., Secretary 

BUREAU OF MINES 
T S Ary, Director 







Library of Congress Cataloging in Publication Data: 



Chilton, J. E. 

A personal miner's carbon monoxide alarm / by J.E. Chilton and C.R. Carpenter. 

p. cm. - (Information circular / United States Department of the Interior, 
Bureau of Mines) 

Bibliography: p. 10 

Supt. of Docs, no.: I 28.27:9233. 

1. Mine gases-Analysis-Equipment and supplies-Testing. 2. Carbon monoxide- 
Analysis-Equipment and supplies-Testing. 3. Gas-detectors-Testing. I. Carpenter, 
C. R. (Clarence R.) II. Title. III. Series: Information circular (United States. 
Bureau of Mines) 

TN295.U4 [TN305] 622 s-dc20 [622'.82] 89-600201 CIP 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Exposure to carbon monoxide 2 

Measurement of carbon monoxide 4 

Prototype carbon monoxide alarm characteristics 4 

Prototype personal miner's carbon monoxide alarm 5 

Test method 6 

Test results 6 

Humidity effects 6 

Gas interferents to disk reaction 6 

Temperature effects 8 

Variability 9 

Conclusions 10 

References 10 

Appendix.-Electrical schematic and component list for PEMCOAL 2 11 

ILLUSTRATIONS 

1. Formation of carboxy-hemoglobin by carbon monoxide exposure 3 

2. Effect on health by exposure to carbon monoxide . 3 

3. PEMCOAL 2 electrical function diagram 5 

4. PEMCOAL 2 5 

5. Apparatus for test of carbon monoxide alarm 7 

6. Effect of carbon monoxide concentration and humidity on PEMCOAL alarm times 7 

7. Effect of hydrogen sulfide and carbon monoxide on PEMCOAL 1 alarm times 7 

8. Effect of temperature on PEMCOAL alarm times 8 

9. Proposed reaction sequences for palladium chloride with carbon monoxide and water 8 

10. Effect of lot number on response of CO reactive disk 9 

A-l. Electrical schematic for PEMCOAL 2 12 

TABLE 

A-l. Electrical components for PEMCOAL 2 11 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


A 


ampere 


MF 


microfarad 


°C 


degree Celsius 


mg/kg 


milligram per kilogram 


ft 


foot 


min 


minute 


ft 3 


cubic foot 


mL/min 


milliliter per minute 


g 


gram 


Mohm 


megohm 


h 


hour 


pet 


percent 


in 


inch 


ppm 


part per million 


kohm 


kilohm 


ppm/min 


part per million per minute 


lb 


pound 


s 


second 


mA 


milliampere 


V 


volt 


mA-h 


milliampere-hour 







A PERSONAL MINER'S CARBON MONOXIDE ALARM 

By J. E. Chilton 1 and C. R. Carpenter 2 



ABSTRACT 

Underground miners may be exposed to hazardous quantities of toxic gases, such as carbon monoxide 
(CO), generated from mine fires or explosions. Every underground miner is required to carry a filter 
self-rescuer (FSR), which when operated will remove CO from the miner's breathing air. In addition, 
every underground miner must have a self-contained self-rescuer (SCSR) near the worksite that will 
supply breathing oxygen. In many situations, miners do not know when to don either rescuer since 
they do not know if there is a fire in the mine, nor do they carry instrumentation necessary for the 
detection of the toxic, colorless, and odorless fire product CO. If each miner carried a personal CO 
alarm, which would respond to high concentrations of CO, the miner would then be alerted when to don 
either the FSR or SCSR and exit the mine. A prototype personal miner's CO alarm called PEMCOAL 
was developed by the U.S. Bureau of Mines. The PEMCOAL unit is small enough to be carried on 
a miner's belt, has a flash lamp visual alarm, requires no calibration for use, and uses a chemical sensor 
that changes color by reaction with trace quantities of CO. The chemical sensor was tested at 
concentrations of CO from 10 to 1,000 ppm, at temperatures from 5° to 40° C, and with several potential 
mine gas interferents. The PEMCOAL alarm times were sufficiently fast to warn miners before they 
are exposed to hazardous quantities of CO. 



Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



Miners could be exposed to significant quantities of CO 
during their work experience. Coal mines may contain 
endogenous CO, which is produced by air oxidation of 
pyrophoric coal. Fires in mines involving coal, wood, and 
belting materials will produce CO as one of the principle 
components in the initial fire stage. Diesel-powered 
engines produce CO as one constituent of the exhaust, and 
explosive fumes from blasting also contain substantial 
quantities of CO. 

This universality of potential exposure to CO was 
recognized by the Mine Safety and Health Administration 
(MSHA) in promulgating rules that require every under- 
ground miner to carry a belt-mounted self-rescuer. This 
FSR is intended to be used in case of a mine fire or 
explosion to remove CO from breathing air. The FSR 
catalytically oxidizes the CO to form relatively innocuous 
carbon dioxide (C0 2 ). Thus, by timely use of the FSR, 
the miner can breath air purified of CO while leaving the 
mine. This use of the FSR tacitly assumes that the con- 
taminated air still contains sufficient oxygen for the miner 
to breathe. Recognizing that substantial amounts of 
oxygen may be consumed in large mine fires, and that the 
fire may produce large quantities of toxic products so that 
the miner cannot breath the air filtered by the FSR, 
MSHA now requires, in addition, that all miners have a 
SCSR stored in close proximity to their workplaces. This 
SCSR contains either a pressurized oxygen supply or an 
oxygen-generating chemical to provide a 1-h supply of 
breathing oxygen for the miner to use while leaving a 
contaminated area in the mine. 

Although a miner may have an FSR and an SCSR on 
hand, the miner will not be protected from exposure to 
CO unless the devices are actually used. Obviously, if 



miners can see the active mine fire or survive a mine 
explosion, they will be prompted to use the breathing units 
and leave the area. If, however, the miners are not within 
sight of the fire, they will have to rely on receiving that 
information from others. Usually after a fire is discovered, 
a fire alarm is actuated and the mine supervisor is notified. 
The supervisor will verify that there is a fire and, based 
on the size and intensity of the fire, will have the miners 
exit the mine or stay and fight the fire. This decision will 
be sent to the affected miners at various work locations. 
This may be the first time that some miners are aware 
that there is a fire and that breathing devices should be 
donned. The problems inherent in this complicated super- 
visory process and the likelihood of breaking this chain of 
logical steps was, unfortunately and tragically, illustrated by 
the Wilberg Mine fire near Orangeville, UT, in December 
1984, when 27 miners and management observers died 
when some of them failed to don their SCSR's in time or 
could not activate them to escape from the mine fire. 

As a direct result of this mine accident, MSHA has 
issued rules requiring hands-on training of underground 
coal miners in the use of SCSR's. Through this training 
miners will know how to quickly don their SCSR's; how- 
ever, in addition, they will still need to know when to use 
them. One technique of insuring the timely use of the 
FSR's or SCSR's is to have all miners carry a personal 
CO alarm to inform them that they are exposed to high 
concentrations of CO and thus, prompt the miners to don 
their breathing apparatus. This U.S. Bureau of Mines 
report will examine the characteristics of PEMCOAL, 
which will help the miner to know when the FSR or SCSR 
should be used. 



EXPOSURE TO CARBON MONOXIDE 



The concentrations of CO to which an underground 
coal miner is normally exposed during the work-shift 
ranges from 2 to 4 ppm for West Virginia and Pennsyl- 
vania mines, to 8 to 10 ppm for Illinois and western 
Colorado mines. The sources for this CO include air 
oxidation of coal and CO in the mine ventilation intake 
air from surface sources. Undiluted mine diesel engine 
exhaust CO concentrations can range from 200 ppm for 
well maintained equipment to an MSHA limit of 2,500 
ppm (7). 3 The ventilation air-diluted CO concentrations 
measured in several mines range up to 20 ppm; the MSHA 
limit for diluted diesel exhaust gas is 100 ppm CO. Coal 
mines using explosives may typically fire 30 lb of explosives 
per round, which generate an average of 9 ft 3 of CO (2). 



3 Italic numbers in parentheses refer to items in the list of references 
preceding the appendix at the end of this report. 



If this were mixed with air in a typical heading with dimen- 
sions of 5 by 20 by 20 ft, a concentration of 4,500 ppm CO 
would be formed. This CO must be diluted to a safe 
working level by fresh air ventilation before the miners 
reenter the section to remove the loose coal. CO 
produced by coal fires may reach concentrations of up to 
3.0 pet (30,000 ppm) or 4.0 pet (40,000 ppm) in mines 
sealed to extinguish the fire. 

Miners may not work in air containing harmful quanti- 
ties of noxious gases, and the concentration of any gas 
shall not exceed the current threshold limit value (TLV) 
for the gas (3). For CO, the TLV is an average concen- 
tration of 50 ppm taken over an 8-h work-shift for a 40-h 
workweek. There is also a short-term exposure limit 
(STEL) for excursions of CO concentrations, which is 
400 ppm CO average concentration over a 15-min period. 
These periods should not be repeated more than four 
times per work-shift (4). The TLV of 50 ppm CO or 



STEL of 400 ppm CO are concentrations to which nearly 
all miners may be repeatedly exposed without adverse 
health effects (5). In addition, the Occupational Safety 
and Health Administration (OSHA) lists an immediate 
danger to life or health (IDLH) concentration which is a 
maximum level from which one could escape within 30 min 
without any escape-impairing symptoms. The IDLH limit 
for CO is 1,500 ppm (<5). 

To summarize, there can be potentially lethal amounts 
of CO generated in mines by many sources, such as fires, 
as well as ever-present small amounts of CO to which 
miners may be exposed without adverse effects. The 
mission of PEMCOAL is to alert the miner only when 
potentially harmful amounts of CO are present so that the 
miner can take appropriate action. This action should take 
place before the miner has been exposed to a sufficient 
amount of CO that would prevent escape. 

CO is absorbed by hemoglobin in the blood to form a 
carboxy-hemoglobin (COHb) compound, which is more 
stable than the oxygen-hemoglobin complex. Thus, the 
ability of the hemoglobin in the blood to supply oxygen to 
vital parts of the body, such as the brain and heart, is 
impaired. The symptoms or response of humans is depen- 
dent on the amount of COHb in the blood as shown in 
figure 1 (7). Generally, no symptoms appear in healthy 
humans at concentrations of COHb less than 10 pet. 
Slight to severe headaches, impairment of judgment, dizzi- 
ness, and shortness of breath occur between 20 to 50 pet 
COHb, unconsciousness from 50 to 60 pet COHb, and 



eventually death at 80 pet COHb. The amounts of COHb 
are correlated to the CO exposure in ppm CO-hours 
where at exposure of 600 ppm-hours and below there are 
no perceptible effects (8). Obviously the exact amount of 
COHb formed in a human at a given concentration of CO 
for a given exposure time is dependent on (1) the breath- 
ing rate and thus the work being performed, (2) the size 
of the human and thus the blood volume, (3) the oxygen 
pressure in air and thus the altitude, and (4) the ambient 
temperature. The differences in exposure conditions and 
in human response account for some of the data variabil- 
ity. Another way of showing the effects of CO on adult 
health as a function of exposure time is given in figure 2 
(9). The MSHA limits for the TLV average concentration 
of 50 ppm CO over a 480 min duration is well below the 
two areas showing adverse symptoms. At the upper range 
of 10,000 ppm CO within 3 to 5 min of exposure, a miner 
could collapse and be in danger of death. The CO alarm 
should operate at a level below the point where any of the 
symptoms of headache, impairment of judgment, dizziness, 
or nausea occur and thus, give an alarm at a level that can 
be located on this graph below and to the left of the curves 
showing these effects. The alarm times determined exper- 
imentally by this work using the prototype PEMCOAL 1 
unit from early data are shown on figure 2. With 1,000 
ppm CO concentration, the alarm occurred in an aver- 
age time of 8 min. Thus, the PEMCOAL unit would 
provide an alarm before onset of the first symptoms of 
CO poisoning. 



1,000 



-Headache and nausea 
Perceptible effect 



500 



6 20 ° 
O 



or 

CO 

o 
a. 
x 

LU 



100 



50 



20- 



-No effect 




•HHn 



1 ; | ■ 

J I I l i i I ll 



20 



50 



I00 



BLOOD COHb, pet 



Figure 1. -Formation of carboxy-hemoglobin by carbon 
monoxide exposure. 



10,000 



5,000 



2,000 



500 



200 — 



100 — 



20 



| 1 1 — I — | I I I I I 1 I I | I i IL 



Collapse, danger 
of death 




OSHA IDLH value 



PEMCOAL 
alarm points 



MSHA limits'] 
-TLV .' 



J i i I i i 1 1 1 I i i I i i 1 1 1 I i i_L 



12 5 10 20 50 100 200 500 1,000 

TIME, min 
Figure 2. -Effect on health by exposure to carbon monoxide. 



MEASUREMENT OF CARBON MONOXIDE 



Several techniques are available for measuring CO in 
the concentration range of 10 to 1,000 ppm. These include 
(1) chemical stain tubes and disks that change color upon 
reaction with CO, (2) electrochemical sensors that mea- 
sure the CO oxidation current, (3) solid-state semicon- 
ductors, such as tin oxide, which change resistance when 
reacted with CO, and (4) infrared (IR) detectors that 
measure light absorption by the CO. The CO stain tubes 
and disks normally rely upon visual examination to warn 
of high levels of CO. However, an automatic alarm is 
preferred to relying on haphazard visual detection of 
the CO indication. Handheld electrochemical CO moni- 
tors with audible and visual [usually light emitting diode 
(LED)] alarms, which are certified by MSHA for intrinsic 
safety, are available from seven manufacturers at an aver- 
age price of $850. In addition to the initial purchase price, 
each monitor will have an annual maintenance cost of $250 
to $300 for the replacement CO sensor, battery, and 



gas calibration supplies. Although these electrochemical 
monitors may now be used for this application by the more 
affluent mining companies, the CO alarm discussed in this 
report will be much less expensive and will not require 
continual calibration during use. Present IR gas monitors 
require large electrical power for operation, are not readily 
portable, and cost $1,500 or more. Semiconductor CO 
detectors require high electrical current for operation, and 
are very sensitive to humidity. To date, none of the elec- 
trochemical, IR, or semiconductor sensors have proven 
applicable to this personal monitor concept because of 
cost or sensitivity. New developments now occurring in 
microsized solid-state sensors may, however, have future 
applications for this CO alarm type. 

The CO alarm discussed in this Bureau report will use 
an optocoupler consisting of an IR LED and a photo- 
sensitive silicon transistor to detect the change in color of 
a chemical disk that reacts with CO. 



PROTOTYPE CO ALARM CHARACTERISTICS 



The PEMCOAL objective is to warn the miners of 
exposure to potentially hazardous quantities of CO. 
Therefore, the alarm must activate before the miner's 
health or judgment is impaired. One goal for this alert 
or alarm level is the OSHA IDLH standard: alarm at a 
concentration of CO of 1,500 ppm before 30 min have 
elapsed (6). Thus, the most critical objective can be met 
if the alarm activates at concentrations of CO lower than 
1,500 ppm of less than 30 min duration. The ability of the 
disk to trigger an alarm at a given time and at a given 
concentration of CO depends entirely upon the properties 
of the chemical reaction of the solid compound with CO. 
These properties include the speed of the overall reaction, 
the arrangement of the reactive chemicals on the substrate 
for rapid interaction of the gas phase CO with the solid 
phase, and the ultimate reaction color change. The test 
program, which is described below, was implemented to 
see if this objective can be met with one type of a com- 
mercially available palladium salt-silica gel system. 

On the other hand, the alarm should not be too sensi- 
tive, causing the miners to needlessly don their breathing 
equipment. Tests were run at background concentrations 
of CO, which are normally encountered in mines to verify 
that false alarms will not be triggered. 

Based on the premise that the PEMCOAL should be 
carried by all miners, (attached to their belt or rescue 
equipment) and that each unit should be inexpensive (cost 
less than $50), the following criteria were used in the unit's 
design: 

S/ze-Smaller in size than a self-rescuer-5 by 3.5 by 2.5 
in. 



Weight-Less than 0.5 lb. 

Calibration-Nol required if each disk is identical, con- 
taining the same amount of the reactive chemical. This 
requirement means that the disk manufacturer should 
have the production system under good quality control. 

Power-9-V low-current alkaline battery, available in 
any mine locality, such as NEDA 4 1604-A. 

Alarm Mode-Strobe light with pulsed operation, effec- 
tive in dark, noisy mines. 

SensingPrinciple-A chemically treated disk that changes 
color by reaction with CO. The disk is obtained from 
commercial, readily available sources. One type of disk 
uses a palladium salt on a silica gel substrate, which is 
initially a straw yellow color and reacts with CO to form 
a gray color. 

Electronic Design-Sense, the disk color change with a 
reflective-type optocoupler containing an IR emitting 
LED and a silicon photo detector. Minimize electrical 
current drain by pulsing or intermittently operating 
both the optocoupler sensor and the alarm light. 



4 Reference to specific products does not imply endorsement by the 
U.S. Bureau of Mines. 



PROTOTYPE PERSONAL MINER'S CO ALARM 



The electronic circuitry and a CO sensing disk were 
assembled into a plastic case suitable for wearing on a 
miner's belt. The electrical function diagram is given in 
figure 3 showing the relationship between the IR diode, 
the CO sensitive disk, and the photosensitive transistor. 
The complete electrical schematic for the most recent 
prototype, PEMCOAL 2, is figure A-l in the appendix. In 
this unit, a reflective optocoupler (TRW OPB 703A) is 
positioned to view the disk during the color change caused 
by reaction with CO. The measured voltage was 2.6 V for 
unreacted disks, and the final voltage was 4.2 V for the 
completely CO reacted disks (dark gray). An alarm 
threshold voltage was chosen at 3.5 V for this application, 
which is almost one-half of the total voltage change. The 
703A reflective device is powered by a pulse generator 
with periods of 0.1 s on and 1.5 s off. The voltage output 
from the silicon phototransistor is compared with the 
reference voltage (3.5 V), and when this voltage is exceed- 
ed, the alarm is latched on until the next pulse sequence 
starts. The prototype unit PEMCOAL 1 alarm is a visible 
red LED and the PEMCOAL 2 alarm is a strobe light 
with greater visual impact. The PEMCOAL 2 strobe light 
and all of the high-voltage components were encapsulated 
in a transparent flexible silicon polymer. This will render 
flash components intrinsically safe for operation in poten- 
tially flammable gas mixtures. The alarm is pulsed with a 
time period of 0.05 s on and 0.5 s off, two flashes per 
second, to conserve the battery power. The battery is a 9- 
V transistor type with a useful capacity of 100 mA-h at 
the 10 h rate of discharge. The average current drain is 
3.1 mA, and it is recommended that a new battery be used 
each week. A secondary Ni-Cd 7.2 V battery may be used 
also with a projected service life over one year. 

To check the operation of the alarm, a plastic holder 
carrying the CO sensitive disk is inserted part of the way 
into the unit until the closing of the spring-loaded turn-on 
switch can be felt. The optical sensor will then view the 
dark inner case wall. With the holder in this position, the 
alarm lamp will flash, thus checking the operating status of 
the electrical circuitry and the battery. The holder with 
the disk is then pushed all of the way into the unit to posi- 
tion the fresh unreacted disk in front of the optocoupler. 
The alarm will then stop flashing as the sensor views a 
fresh unreacted disk and the unit will then be ready for 
use. The prototype unit in figure 4 shows the disk on the 
holder before insertion into the unit. 



IR-diode 
light source 



Phototransistor 
detector 



r^--i 


Pulse 




;..Ol 


generator 




i j Reflective 
1 i optocoupler 












i 






W 


Amplifier 




Comparator 




Alarm 


-1*! 


lHj 



















Transparent plastic 
encapsulation 



Figure 3.-PEMCOAL 2 electrical function diagram. 




Figure 4.-PEMCOAL 2. 



TEST METHOD 



All of the following data were obtained by the PEM- 
COAL 1 unit which was tested in the experimental setup 
shown in figure 5. An environmental chamber was used 
for ambient temperature control. The gas mixtures were 
prepared using compressed cylinders of standard gases 
diluted by air in a dynamic gas mixing system regulated 
by mass flow controllers (10). The test gas mixture was 
humidified using water in a gas washing bottle with a 
fritted disk for bubble dispersion. For tests with water 



soluble gas constituents, only the air diluent was humid- 
ified. The test gas was fed into the CO alarm using a 
plastic hood with gas flow set usually at 400 mL/min. 
Times to alarm were measured with an electronic timer 
containing an optical sensor that stopped the timing cycle 
when the alarm LED was turned on. For all of this work, 
commercially available CO sensitive chemical disks were 
purchased from the American Gas & Chemical Co., 
Northvale, NJ, as Leak-tec CO-50-R CO indicators. 



TEST RESULTS 



Initial experiments with the prototype CO alarm were 
run at 24° C using fresh disks and immediately exposing 
them to a CO test gas. Generally, three test gas concen- 
trations were used: 250, 400, and 1,000 ppm CO mixtures 
in air with 84 pet relative humidity. Alarm times mea- 
sured with the fresh disks are shown in the lower curve in 



figure 6. Average alarm times of 10.94 min were obtained 
with standard deviation of 3.88 min for 250 ppm gas 
challenge. At higher concentrations of CO, the disks 
responded faster with an average alarm time of 2.58 min 
and a standard deviation of 0.98 min for the 1,000 ppm 
CO challenge. 



HUMIDITY EFFECTS 



The disks were found to have a slower response if they 
were initially exposed to air containing water and then 
challenged with CO, simulating their use in wet mines. 
Tests were run for 2 h with humid air (84 pet RH), and 
then the disks were challenged by test gases containing 
CO. The results of these tests are plotted on the upper 
curve in figure 6. The alarm times at 250 ppm CO were 
an average of 49.5 min with a standard deviation of 12.03 
min. At 1,000 ppm CO gas challenge, the alarm times 
were an average of 8.4 min or over 3 times as long as the 
alarm times obtained with the fresh disks. 

Several tests were run with the initial CO test con- 
centration at 10 ppm CO in humid air for 6-h duration, 
simulating typical mine background levels of CO. The 



PEMCOAL unit did not alarm at the 10 ppm CO concen- 
tration level during the 6-h exposure. At the end of each 
test, the unit was then challenged with a higher concen- 
tration of CO. Alarm times of 12 and 16 min were mea- 
sured at 1,000 ppm CO, alarm times of 30 and 36 min at 
400 ppm CO, and alarm times of 78 min at 250 ppm CO 
challenge gas. This test simulated the use of the CO 
alarm by coal miners working in a mine with high humidity 
(84 pet RH) with a background concentration of CO of 
10 ppm, and having a fire occur after they had been work- 
ing for 6 h. The units would still respond before the 
miner was adversely affected by the ambient CO at con- 
centration levels from 250 to 1,000 ppm CO. 



GAS INTERFERENTS TO DISK REACTION 



Several gas interferents to the reaction of CO with 
the chemical disks were examined. The interferent gases 
included hydrogen sulfide (H 2 S) formed in mines by 
reaction of sulfide minerals with acid mine water, sulfur 
dioxide (S0 2 ) generated in mine fires from burning of 
sulfur-containing materials and present in diesel engine 
exhaust from sulfur in the fuel, and nitric oxide (NO) and 
nitrogen dioxide (N0 2 ) both formed in diesel engine 
exhaust and in gas fumes from explosive blasting. 

The PEMCOAL 1 unit was run in air with 50 ppm S0 2 
for 3 h; no alarm was obtained. This exposed disk was 
then challenged with 1,000 ppm CO and an alarm time of 
7 min was measured. This alarm time for the 1,000 ppm 



CO measured after the 3-h exposure to SO z was equivalent 
to the average alarm time of 8 min previously found in 
runs at 1,000 ppm CO after a 2 h exposure to moist air. 
With additional tests at 25 ppm S0 2 and 243 ppm CO, 
alarm time of 18 min was measured. With 5 ppm S0 2 and 
255 ppm CO, alarm times of 7 min and 6.3 min were 
measured. With tests at 255 ppm CO alone, alarm times 
of 9.5 and 8.7 min were obtained. Thus, at a concentra- 
tion of 5 ppm S0 2 there is very little effect on the CO disk 
reaction. The TLV for S0 2 is 2 ppm, and if the mine is 
operating under compliance for allowable toxic gases (3), 
no effect of S0 2 is expected on the CO alarm. 



CO 








Gas 

mixing 
system 






A 






Air 





Plastic cap 




Humidifier 



Temperature-controlled 
environmental chamber 



Figure 5.-Apparatus for test of carbon monoxide alarm. 



IUU 


- 


1 


1 


1 1 


- 




_ 


\ ° 









50 


— 


V 






— 




- 


o 


o 
\ ° 




- 








o 


/ Expose 2h, 
/ 84pctRH 
C air before test 


" 


20 


— 








— 


c 




X 








ALARM TIME, m 

o 


- 


\ : 

X 

X \ 

X ^ 
X 


\ X 

\ X 


^~- Immediate test 


~o 


5 






X 




— 








X 
















X 


2 
1 




1 


1 


1 1 


X 

H 

1! 



200 400 600 

CO CONC, ppm 



800 1,000 



The PEMCOAL 1 unit was run in 7 ppm NO for 3 h 
and no alarm was obtained. This unit was then challenged 
with 7 ppm NO and 250 ppm CO, and an alarm time of 
10.5 min was obtained. When a fresh disk was run in a 
mixture of 7 ppm NO and 242 ppm CO, an alarm time of 
6.2 min was measured. For comparison, a run in 241 ppm 
CO alone had an alarm time of 8.7 min. Thus, the pres- 
ence of NO did not significantly effect the response of the 
CO chemical disk. The TLV for NO is 25 ppm and typical 
concentrations measured in several coal mines with diesel- 
powered equipment are less than 8 ppm NO. 

The PEMCOAL 1 unit was run in 8.9 ppm N0 2 with 
254 ppm CO, and an alarm time of 90 min was measured. 
With 3.6 ppm N0 2 in 248 ppm CO, an alarm time of 29.7 
min was measured. The alarm time for the unit exposed 
to 276 ppm CO alone was 7 min. Thus, N0 2 in these tests 
is an interferent to the reaction of the CO chemical disk. 
The PEMCOAL 2 unit has a dust filter composed of open 
cell porous polyurethane placed over the gas inlet ports. 
This unit had alarm times of 2.9 and 5.7 min when tested 
in 3.6 ppm N0 2 with 248 ppm CO, and when tested with 
3.6 ppm N0 2 with 908 ppm CO had an alarm time of 2.3 
min. Thus, no effect was found on the PEMCOAL 2 unit 
from the N0 2 . In these tests, the foamed plastic filter 
adequately removed the N0 2 from the CO mixture. The 
TLV for N0 2 is 3 ppm and measurements in mines with 
diesel-powered equipment have found concentrations of 
1 ppm or less. 

Tests of the PEMCOAL 1 unit with H 2 S showed a 
strong positive interference to the CO chemical reaction 
(fig. 7), which shows the alarm times obtained at various 
gas concentrations. CO reacts with the sensor disk to 



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10 100 

ALARM TIME, min 



1,000 



Figure 6.-Effect of CO concentration and humidity on the 
PEMCOAL alarm time. 



Figure 7.-Effect of hydrogen sulfide and carbon monoxide on 
PEMCOAL 1 alarm times. 



H 2 S reacts with the sensor 



form gray palladium metal 

disk to form black colored palladium sulfide 

more sensitive to H 2 S by a factor of 2 over the CO. If a 



mine atmosphere contained H 2 S, a chemical filter contain- 
ing zinc, lead, or mercury salts would be added to the unit 
to remove the interferent. The TLV for H 2 S is 10 ppm 
and at this concentration an alarm time of 55 min would 
be obtained with the CO reactive disk. 



To summarize the effect of gaseous interferents on 

The disk is the CO disk reaction, significant quantities of N0 2 would 

increase the alarm times and H 2 S would shorten the alarm 



times for the CO detection, while both S0 2 and NO would 
give minimal effects at the low concentrations expected 
in mines. 



TEMPERATURE EFFECTS 



The effect of ambient temperature on the alarm times 
was measured from 5° to 40° C as presented in figure 8. 



100 




10 20 30 

TEMPERATURE, °C 

Figure 8. -Effect of temperature on PEMCOAL alarm times. 



The alarm times were quicker at the higher temperatures 
for all three gas concentrations. At 5° C and with 250 ppm 
CO challenge gas, several of the tests did not alarm in 100 
min. When the disks were removed from the test fixture, 
the disks were still the original light straw yellow color, but 
turned dark gray as the disks were, warmed in air. This 
observation leads to the conclusion that the disks adsorb 
the CO at the low temperature, but the subsequent reac- 
tion of the adsorbed CO with palladium ion to produce the 
metallic palladium is slow at low temperatures. 

The slow reaction of CO with palladium salts at low 
temperature, and the slow reaction in the presence of 
excess water may be explained by the hypothesized reac- 
tion sequences presented in figure 9. The interaction of a 
palladium chloride coordinated complex with water and 
CO is indicated. The equilibrium constant for the forma- 
tion of the palladium-water complex is probably greater 
than the equilibrium constant for the palladium CO-water 



H 

I 
H — 0. CI. CI 

^Pd Pd 

CI *CI * — H 

I 

H 



I + 2H0H z^: 2 



Initial 


palladium 
I 


salt 


(straw yellow) 




H 

1 






1 
H-0 

CI' 


Pd 


-H 



1 + 2 CO 



n 



CO. CI 

•pdf 

Cl^ *0 — H 



IE 



H 



hi 



Pd°+ C0 2 + 2 HCI 

(gray- 
black ) 



Figure 9. -Proposed reaction sequences for palladium chloride 
with carbon monoxide and water. 



mixed complex because of the loss of reactivity of the 
palladium complex in the presence of excess water. By 
storing unreacted disks over concentrated sulfuric acid the 
water was removed from the disks and the disks changed 



color from the pale straw yellow color to a darker orange 
color. The dried disks did not react with dry 1,000 ppm 
CO during tests for an hour. Thus, some water is neces- 
sary for the reaction of the palladium compound with CO. 



VARIABILITY 



The CO reactive disks were purchased in lots contain- 
ing 10 plastic sealed disks. To determine the alarm time 
variance for the disks within a lot and the alarm time 
variance from lot to lot, data were collected from tests of 
disks with 250 and 1,000 ppm CO exposure. A plot of the 
disk lot numbers versus the products of the CO test con- 
centration with the measured alarm time is given in fig- 
ure 10. If the reaction rate for the formation of palladium 
metal is a function of the CO concentration, the amount 
of palladium formed is proportional to the product of the 
CO concentration and the alarm time. If the palladium 
metal is uniformly spread over the disk, a given amount of 
palladium will form a fixed optical density change on the 
disk. Since the disk color density for alarm is a constant 
determined by the optocoupler characteristics and by 
the alarm set voltage, the products of the gas concen- 
tration and the alarm time should be a constant. The 
average value for the products measured at 250 ppm CO 
is 2,087 ppm min with a standard deviation of 540 ppm 
min or a relative standard deviation of 25.9 pet. The 
average value for the products measured with 1,000 ppm 
CO is 2,278 ppm min with a standard deviation of 498 ppm 
min or a relative standard deviation of 21.9 pet. These lot- 
to-lot relative standard deviations (coefficient of variances) 
are of the same magnitude as the within-lot relative stan- 
dard deviations for lot 27 of 22.6 and 15.5 pet. An analysis 
of variance test was run on the data from the different lots, 
and there was no significant difference between the lot-to- 
lot variances and the within-lot variances. The product 
values for lot 27 seem to fall below the lot average values 
indicating that these disks may be more sensitive to CO; 
however, the values are within the three sigma range for 
normal scatter of data. 

The range of data in figure 10 shows that at 1,000 ppm 
CO exposure the alarm times varied from 1.6 to 3.2 min. 
Some of the disk alarm time variation may be due to 
different amounts of palladium material on the disks. 
Chemical analysis for palladium by inductively coupled 
plasma emission was performed on extracts from four 



disks, two from lot 17 with high sensitivity and two from 
lot 22 with lower sensitivity (longer alarm times). The 
weight of palladium plus silica material on each disk is 
approximately 0.1 g. For lot 17, the average amount of 
palladium was 1,530 mg/kg of material with a standard 
deviation of 99 mg/kg and for lot 22 the average was 
1,385 mg/kg of material with a standard deviation of 
21 mg/kg. Since the difference between these analyses 
are not statistically significant, other factors than total 
palladium content may affect the disk response times, 
such as the type and amount of silica gel binder and the 
uniformity of the metal deposits on the disk surface. 
Good quality control measures must be taken by the 
manufacturer to assure a consistent and uniform response 
to CO for each of the disks. 



35 



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cr 

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15 



o o oo 
.. o 



x o 

o 



KEY 
x 1 ,000 ppm CO 
o 250 ppm CO 



10 15 20 

LOT NUMBER 



25 



30 



disk. 



Figure 10.-Effect of lot number on response of CO reactive 



10 



CONCLUSIONS 



A prototype personal miner's CO alarm has been de- 
signed and fabricated using a commercial solid chemical 
disk, which changes color in the presence of CO. This 
prototype alarm is designed to warn a miner of exposure 
to potentially harmful amounts of CO before the miner 
can experience adverse health effects. Operation of two 
models, PEMCOAL 1 and 2, have been tested at CO 
concentrations to 1,000 ppm where the alarm times range 
from 2 to 3 min for tests at room temperature. The cost 
of parts purchased singly for the unit are under $40, and 
if the primary transistor battery and the disk were changed 
each week, the unit would incur an additional maintenance 
charge of $1.75 weekly. In the event of a mine disaster 
generating a large amount of CO, the use of this unit to 
warn a miner to don protective breathing equipment and 
exit the mine would substantially improve the miner's 
chance of survival. 



Successful operation of the CO alarm in mines depends 
critically upon a reliable source of reproducible disks. 
Thus, it is necessary to obtain data on the disk quality 
control, or alternately, to find a separate source of high- 
quality CO reactive disks. The present CO alarm uses a 
palladium salt to react with the CO. The chemistry of 
other potentially CO reactive compounds should be exam- 
ined to find alternate color-changing reactions which may 
be more sensitive and more reversible. Gaseous inter- 
ferents to the operation of the CO reactive disks such as 
H 2 S were verified and techniques can be devised to remove 
these interferences for in-mine use. Ultimately, in-mine 
tests need to be conducted for testing of durability and for 
identifying potential problems caused by operation in the 
presence of water aerosol and coal dust. 



REFERENCES 



1. U.S. Code of Federal Regulations. Title 30-Mineral Resources; 
Chapter I-Mine Safety and Health Administration, Department of 
Labor; Subchapter E-Mechanical Equipment for Mines; Part 32 Mobile 
Diesel-Powered Equipment, sec. 32.4 (f) (1); July 1, 1987, p. 204 

2. Garcia, M. M., E. P. Jucevic, and W. C. Kjttrell. Monitoring of 
Gases From Explosives Detonated in an Underground Mine (contract 
HO395098, Univ. AZ). BuMines OFR 72-83, June 1982, 81 pp.; NTIS 
PB 83-191718. 

3. U.S. Code of Federal Regulations. Title 30-Mineral Resources; 
Chapter I-Mine Safety and Health Administration, Department of 
Labor. Subchapter O-Coal Mine Health and Safety-Part 56-Subpart 
Coal Mine Safety and Health, Part 75 Manditory Safety Standards- 
Underground Coal Mines, Subpart D, sec. 75.301-2, July 1, 1985, p. 444. 

4. American Conference of Governmental Industrial Hygienists 
(Cincinnati, OH). Threshold Limit Values and Biological Exposure 
Indices for 1988-1989. 1988, 116 pp. 



5. American Conference of Governmental Industrial Hygienists 
(Cincinnati, OH). Documentation of the Threshold Limit Values for 
Substances in Work Room Air. 1971, pp. 41-43. 

6. National Institute for Occupational Safety and Health. NIOSH 
Pocket Guide to Chemical Hazards. DHEW publ. 78-210, Sept. 1985, 
p. 72. 

7. Sax, N. I. Dangerous Properties of Industrial Materials. Van 
Nostrand Reinhold, 4th ed., 1975, p. 520. 

8. National Institute for Occupational Safety and Health (Cincinnati, 
OH). Criteria for a Recommended Standard Occupational Exposure 
to Carbon Monoxide. 1972, 110 pp. 

9. Slusher, G. R. An Evaluation of Low Cost Carbon Monoxide 
Indicators. FAA Tech. Rep. ADS-80, 1966, p. 14. 

10. Carpenter, C. R., J. E. Chilton, and G. H. Schnakenberg, Jr. A 
Dynamic Gas-Mixing System. BuMines IC 8934, 1983, 30 pp. 



11 



APPENDIX.-ELECTRICAL SCHEMATIC AND COMPONENT LIST FOR PEMCOAL 2 

Table A-l is a listing of the electrical components and figure A-l is the electrical schematic for the PEMCOAL 2. 



B 

CI, C2 

C3 

C4, C5 

Dl, D2, D3 

D4 

D5 

F 

J 

N 

Rl 

R2 

R3 

R4 

R5 

R6 

R7 

R8, R9 

RIO 

Rll 

R12 

R13 

R14, R15 

R16 

R17 

R18 

R19 

R20 

R21 

R22 

R23 

R24 

S 

Tl 

T2 

T3, T4 

T5 

Ul, U2 

Z 

'See figure A-l. 

2 Kit C 35655, Edmond Scientific. 



Battery, 


9-V, NEDA 1604 A. 


Capacitor, 1-^F. 


Capacitor, 4-/zF. 


Capacitor, 0.01-/iF. 


Diode, 1N645. 


Diode, 1N4002. 


Diode, 1N4007. 


Flash tube. 2 


Optocoupler, OPB 702A (TRW). 


Neon bulb, NE. 


Resistor 


10-kohm. 


Resistor 


2.2-kohm. 


Resistor 


270-kohm. 


Resistor 


10-kohm. 


Resistor 


1-kohm. 


Resistor 


390-kohm. 


Resistor 


30-kohm. 


Resistor 


4.7-kohm. 


Resistor 


2.2-kohm. 


Resistor 


1-Mohm. 


Resistor 


1-kohm. 


Resistor 


100-kohm. 


Resistor 


1-kohm. 


Resistor 


100-kohm. 


Resistor 


1.47-kohm. 


Resistor 


15-kohm. 


Resistor 


10.5-kohm. 


Resistor 


22- to 47-ohm, adjustable. 


Resistor 


3-kohm. 


Resistor 


100-kohm. 


Resistor 


3.9-Mohm. 


Resistor 


1-Mohm. 


Switch, ] 


L-SM-1. 


Transisti 


K. 2N2222. 


Transisti 


3r. 2N2707. 



Transistor. 2N2222. 

Transistor, SCR, 24 NEC. 

Transformer. 2 

Transparent silicone elastomer, Sylgard 182 (Dow Corning). 



12 



v- 



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Figure A-1. -Electrical schematic for PEMCOAL 2. See table A-1 for a description of components. 



INT.BU.OF MINES,PGH.,PA 29031 



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